Androgens regulate prostate cancer cell growth via an AMPK-PGC-1α-mediated metabolic switch.

Prostate cancer is the most commonly diagnosed malignancy among men in industrialized countries, accounting for the second leading cause of cancer-related deaths. Although we now know that the androgen receptor (AR) is important for progression to the deadly advanced stages of the disease, it is poorly understood what AR-regulated processes drive this pathology. Here we demonstrate that AR regulates prostate cancer cell growth via the metabolic sensor 5'-AMP-activated protein kinase (AMPK), a kinase that classically regulates cellular energy homeostasis. In patients, activation of AMPK correlated with prostate cancer progression. Using a combination of radiolabeled assays and emerging metabolomic approaches, we also show that prostate cancer cells respond to androgen treatment by increasing not only rates of glycolysis, as is commonly seen in many cancers, but also glucose and fatty acid oxidation. Importantly, this effect was dependent on androgen-mediated AMPK activity. Our results further indicate that the AMPK-mediated metabolic changes increased intracellular ATP levels and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α)-mediated mitochondrial biogenesis, affording distinct growth advantages to the prostate cancer cells. Correspondingly, we used outlier analysis to determine that PGC-1α is overexpressed in a subpopulation of clinical cancer samples. This was in contrast to what was observed in immortalized benign human prostate cells and a testosterone-induced rat model of benign prostatic hyperplasia. Taken together, our findings converge to demonstrate that androgens can co-opt the AMPK-PGC-1α signaling cascade, a known homeostatic mechanism, to increase prostate cancer cell growth. The current study points to the potential utility of developing metabolic-targeted therapies directed toward the AMPK-PGC-1α signaling axis for the treatment of prostate cancer.

A dosage-dependent pleiotropic role of Dicer in prostate cancer growth and metastasis.

Dicer is an RNase III enzyme essential for the maturation of the majority of microRNAs. Recent studies have revealed downregulation or hemizygous loss of Dicer in many tumor models and demonstrated that suppressing Dicer activity enhances tumorigenic activities of lung and breast cancer cells, which support Dicer as a haploinsufficient tumor suppressor in these cancer models. Surprisingly, we found that knocking down Dicer expression suppresses the growth and tumorigenic capacity of human prostate cancer cell lines, but enhances migratory capacities of some prostate cancer cell lines. Dicer is upregulated in human prostate cancer specimens, but lower Dicer expression portends a shorter time to recurrence. Complete ablation of Dicer activity in a Pten null mouse model for prostate cancer significantly halts tumor growth and progression, demonstrating that microRNAs have a critical role in maintaining cancer cell fitness. In comparison, hemizygous loss of Dicer in the same model also reduces primary tumor burden, but induces a more locally invasive phenotype and causes seminal vesicle obstruction at high penetrance. Disrupting Dicer activity leads to an increase in apoptosis and senescence in these models, presumably through upregulation of P16/INK4a and P27/Kip1. Collectively, these results highlight a pleotropic role of Dicer in tumorigenesis that is not only dosage-dependent but also tissue context-dependent.

The emerging role of the PI3-K-Akt pathway in prostate cancer progression.

The PI3-K-Akt pathway plays a central role in the development and progression of prostate cancer and other malignancies. We review original studies and summarize relevant sections of previous reviews concerning the relationships between abnormalities in the PI3-K-Akt pathway and prostate cancer progression. We discuss laboratory and clinical data that indicate gene perturbation and dysregulation of PI3-K-Akt pathway is common in prostate cancer and other malignancies. We further discuss the critical role of the PI3-K-Akt pathway in the oncogenic signaling network and provide examples that establish the PI3-K-Akt pathway as a focal point for the future development of informative biomarkers and effective therapies for prostate cancer.

Chromosome 10 alterations in prostate adenocarcinoma (review).

Inactivations of tumor suppressor genes are the most common genetic alterations in prostate adenocarcinoma. Such inactivations are frequently accompanied by loss of portions of the chromosome on which the tumor suppressor gene resides. Loss of portions of both 10p and 10q have been identified in a significant percentage of prostate carcinomas, as well as other malignant neoplasms, and such losses are associated with advanced clinical stage and aggressive behavior in these neoplasms. The PTEN tumor suppressor gene has recently been identified as an important tumor suppressor gene at 10q23. This gene encodes a dual specificity protein phosphatase which interacts with and controls the tyrosine phosphorylation of focal adhesion kinase (FAK), a key regulator of signal transduction via focal adhesions. Such focal adhesions are the site at which integrins cluster following interactions with extracellular matrix ligands and interact with both cytoskeletal proteins and signal transduction molecules to effect key processes such as cell migration, spreading and proliferation. The PTEN gene is inactivated in a significant proportion of prostate carcinomas, particularly metastatic prostate cancers. There is also evidence from studies of loss of heterozygosity that at least one additional tumor suppressor gene for prostate cancer is present on the distal portion of 10q. Similarly, both functional studies and direct analysis of human tumors strongly support the idea that at least one, and possibly two, tumor suppressor genes for prostate cancer are present on 10p. Given that inactivations of tumor suppressor genes on chromosome 10 are associated with advanced clinical stage in prostate cancer these genes are attractive candidates both as prognostic markers and as potential targets for therapeutic intervention.

Sporadic breast cancers exhibit loss of heterozygosity on chromosome segment 10q23 close to the Cowden disease locus.

Cowden disease, a dominantly inherited syndrome characterized by a variety of proliferative lesions and predisposition to breast and thyroid cancer, has recently been linked to the polymorphic marker D10S215 on chromosome segment 10q23. Loss of heterozygosity in prostate cancer is linked to the same marker, whereas loss of heterozygosity in glioblastoma, endometrial cancer, and other malignancies also localizes to this region. Most recently, a putative tumor suppressor gene (PTEN/MMAC1) has been identified in the region between D10S215 and an adjacent, more telomeric marker (D10S541) and was found to be altered in breast cancers, prostate cancers, and glioblastomas. We examined 22 invasive breast cancers for loss of heterozygosity in the 10q23 region and found loss in 41% (9/22). There were two distinct regions of loss, including one near the D10S541 marker, with an approximately equal frequency of deletion in each. The observed pattern of deletion is consistent with the presence of a tumor suppressor gene between D10S215 and D10S541. Most of the poorly differentiated carcinomas in the case collection showed loss of heterozygosity in the region near D10S215, suggesting that this loss correlates with a poor prognosis.

Allelic loss on chromosome 13q in human prostate carcinoma.

To clarify the role in prostate tumorigenesis played by loss of the three known or putative tumor suppressor loci on the centromeric portion of chromosome 13q, we examined 80 clinically localized and 15 advanced prostate carcinomas for allelic loss at microsatellite markers mapped to this region, including markers tightly linked to the BRCA-2, retinoblastoma (Rb), and DBM (deleted in B-cell malignancy) loci. Among the 80 clinically localized cases, 24 showed allelic loss at one or more 13q loci. In all cases with loss, the Rb and/or DBM loci were lost. No cases were found with loss of Rb without loss of DBM or loss of DBM without loss of Rb, implying a role for both the Rb and DBM loci in clinically localized prostate cancer. Loss of the BRCA-2 locus was less common (4 of 55 informative cases) and was always associated with loss of Rb and/or DBM loci. Thus, the BRCA-2 locus does not appear to play as important a role in clinically localized prostate cancer as the Rb and/or DBM loci. Allelic loss on 13q was extremely common in the clinically advanced cases; it was present in 14 of the 15 cases. The rate of allelic loss at each of the three tumor suppressor loci was increased significantly in the advanced cases (P < 0.01, Fisher's exact test). Thus, loss of heterozygosity on 13q is very common in prostate cancer and occurs at all three known or putative tumor suppressor loci on the centromeric portion of chromosome 13q.

Loss of heterozygosity on chromosomes 10 and 17 in clinically localized prostate carcinoma.

Loss of heterozygosity (LOH) at chromosomal loci has been associated with the presence of tumor suppressor genes at the deleted loci. Twenty-six clinically localized, Stage B prostate carcinomas were analyzed for LOH on chromosomes 10 and 17 using microsatellite markers. Two of 26 carcinomas showed LOH on 17p while one showed LOH on 17q. Chromosome 10 showed a complex pattern of LOH with monosomy (1 case), LOH on 10p (1 case), proximal 10q (1 case) and distal 10q (2 cases). Overall 29% of informative cases showed LOH on chromosome 10. These results are consistent with the presence of a tumor suppressor for prostate cancer on 17p and multiple tumor suppressor genes on chromosome 10.

Alterations of the retinoblastoma gene in clinically localized, stage B prostate adenocarcinomas.

Alterations of the retinoblastoma (Rb) tumor suppressor gene and its encoded protein have been detected in a variety of malignant neoplasms. The authors have evaluated a series of 26 clinically localized stage B prostate adenocarcinomas for loss of heterozygosity (LOH) at 13q14 (including the Rb locus), rearrangements or partial deletions of the Rb gene, and alterations of Rb protein level by quantitative immunohistochemistry. LOH at the Rb locus occurred in 35% of the informative specimens. Of the specimens that showed LOH, 33% also had decreased or absent Rb protein in tumor cells by quantitative immunohistochemistry. In contrast, none of the specimens without LOH showed loss of Rb protein. Thus, LOH is correlated with loss of Rb protein. The authors conclude that alterations of the Rb tumor suppressor gene occur in a significant fraction of stage B prostate adenocarcinomas.

Cell cycle control of the BN51 cell cycle gene which encodes a subunit of RNA polymerase III.

The BN51 cell cycle gene complements a temperature-sensitive cell cycle mutation of BHK-21 cells which leads to arrest in G1 at the nonpermissive temperature. Recent evidence indicates it encodes an essential subunit of RNA polymerase III. The BN51 gene is induced 4-fold 4-h after stimulation of quiescent, serum-starved fibroblasts with serum. This induction is abolished by the addition of the protein synthesis inhibitor cycloheximide. Nuclear runoff and transient transcription assays reveal a 2-3-fold increase in transcription in response to serum. There is a comparable 4-fold increase in BN51 protein synthesis following serum stimulation of quiescent fibroblasts. Loss of biologically active BN51 protein increases transcription from the BN51 promoter approximately 3-fold by transient transfection analysis. However, excess BN51 protein or the v-raf oncogene had no effect on transcription from the BN51 promoter in transient transfections. The pattern of transcription of the BN51 gene is similar to the delayed early response genes, which are induced several h after serum stimulation of quiescent cells.

A retrovirus carrying the K-fgf oncogene induces diffuse meningeal tumors and soft-tissue fibrosarcomas.

The K-fgf/hst oncogene encodes a growth factor of the fibroblast growth factor (FGF) family and transforms cells through an autocrine mechanism which requires extracellular activation of its receptor(s). To identify the cell and tissue targets of K-fgf oncogenic potential in vivo, we constructed a recombinant retrovirus carrying the human K-fgf cDNA and injected it, together with helper Moloney murine leukemia virus, into immunocompetent as well as nude mice. The original construct was highly transforming in tissue culture but produced no detectable pathologies in vivo with the exception of a single fibrosarcoma which arose after a long latency. The virus produced by this tumor appears to have undergone a complex series of recombination events involving the helper Moloney murine leukemia virus. It encodes an Env/K-FGF fusion protein whose expression is under the control of a hybrid long terminal repeat. This virus (designated MFS, for meningeal fibrosarcoma) induces tumors in mice with high frequency and short latency. These neoplasms consist of aggressive fibrosarcomas of soft tissue as well as diffuse meningeal tumors originating from the dura mater that surround the whole central nervous system and cause severe hydrocephalus. The Env/K-FGF fusion protein expressed by the MFS virus has retained all of the biological properties of native K-FGF, including secretion, mitogenic activity, heparin binding, and neutralization by anti-K-FGF antibodies. These and other results indicate that the tumors induced by the MFS virus result from the oncogenic potential of K-FGF.

Heterogeneity of very-low-density lipoprotein remnants bound and taken up by liver of starved rat in vivo.

Very-low-density lipoprotein (VLDL), labelled in vivo with [9,10-3H]oleate, was taken up rapidly by liver after injection in vivo. Initially, radioactive lipoprotein remnants in the VLDL density range were present in liver as a bound extracellular pool that could be released by perfusion with polyphosphate or heparin. The bound remnant showed a decrease in mean diameter and an increased proportion of cholesteryl ester as a function of time after injection. When VLDL of different mean diameters was injected, it was found that: (1) total uptake by liver was independent of diameter; (2) small VLDL was not taken up more rapidly than large VLDL; and (3) Large VLDL lost no more triacylglycerol before binding than did small VLDL and larger species of mean diameter greater than 40 nm were bound. It is concluded that there is no unique VLDL remnant taken up by liver in vivo. When livers were perfused after binding radioactive VLDL in vivo, the lipoprotein was metabolized, with the production of water-soluble products, and this metabolism was inhibited by chloroquine.

Endocytosis of very low density lipoprotein remnants by liver of fasted rats.

Radioactive lipoproteins in the very low density lipoprotein (VLDL) density range were taken up by rat liver in vivo. The radioactivity became associated with an intracellular particle of d = 1.11 that did not correspond to lysosomes, endoplasmic reticulum, or plasma membrane as determined by marker enzyme distribution. Radioactive VLDL remnants could be released from these particles by passage through a hydraulic press, hypotonic shock, or sonication. The release of radioactivity from the particles by one of these methods became more complete with increasing time after injection. The injection of colchicine inhibited the breakdown of the VLDL triglyceride and cholesterol ester and caused an accumulation of radioactive material in the d = 1.11 particles. In contrast, injected chloroquine inhibited breakdown of VLDL triglyceride and cholesterol ester and caused an accumulation in lysosomes. We have concluded VLDL remnants are metabolized in liver by an endocytosis-lysosomal digestion pathway and that the d = 1.11 particles are endocytic vesicles. The existence of a releasable pool of VLDL within endocytic vesicles makes it possible to examine the internalized remnant.